X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=src%2Flib.4th;h=efadf95e56ffdd6c71902deef010ad7cff5a4d76;hb=e8fdb1e66ea6d3790e7b7d7b44676418c0081626;hp=b7cd560d2a512ad17797e8bcd29b48eec5e53239;hpb=21567de9ac591909bb28a454b03615a473917327;p=forth.jl.git diff --git a/src/lib.4th b/src/lib.4th index b7cd560..efadf95 100644 --- a/src/lib.4th +++ b/src/lib.4th @@ -1,37 +1,37 @@ : / /MOD SWAP DROP ; : MOD /MOD DROP ; +: */ -ROT * SWAP / ; -: '\n' 10 ; -: BL 32 ; - -: CR '\n' emit ; -: SPACE BL emit ; - -: NEGATE 0 swap - ; +: NEGATE 0 SWAP - ; : TRUE -1 ; : FALSE 0 ; : NOT 0= ; -: LITERAL IMMEDIATE ' LIT , , ; +: CELLS ; \ Allow for slightly more portable code -: ':' - [ - CHAR : - ] - LITERAL -; +: DEPTH PSP@ PSP0 @ - ; +: '\n' 10 ; +: BL 32 ; + +: LITERAL IMMEDIATE ' LIT , , ; + +: ':' [ CHAR : ] LITERAL ; : ';' [ CHAR ; ] LITERAL ; : '(' [ CHAR ( ] LITERAL ; : ')' [ CHAR ) ] LITERAL ; +: '<' [ CHAR < ] LITERAL ; +: '>' [ CHAR > ] LITERAL ; : '"' [ CHAR " ] LITERAL ; : 'A' [ CHAR A ] LITERAL ; : '0' [ CHAR 0 ] LITERAL ; : '-' [ CHAR - ] LITERAL ; : '.' [ CHAR . ] LITERAL ; -\ While compiling, '[COMPILE] word' compiles 'word' if it would otherwise be IMMEDIATE. +: CR '\n' emit ; +: SPACE BL emit ; + : [COMPILE] IMMEDIATE WORD \ get the next word FIND \ find it in the dictionary @@ -39,38 +39,17 @@ , \ and compile that ; -\ RECURSE makes a recursive call to the current word that is being compiled. -\ -\ Normally while a word is being compiled, it is marked HIDDEN so that references to the -\ same word within are calls to the previous definition of the word. However we still have -\ access to the word which we are currently compiling through the LATEST pointer so we -\ can use that to compile a recursive call. : RECURSE IMMEDIATE LATEST @ \ LATEST points to the word being compiled at the moment >CFA \ get the codeword , \ compile it ; -\ CONTROL STRUCTURES ---------------------------------------------------------------------- -\ -\ So far we have defined only very simple definitions. Before we can go further, we really need to -\ make some control structures, like IF ... THEN and loops. Luckily we can define arbitrary control -\ structures directly in FORTH. -\ -\ Please note that the control structures as I have defined them here will only work inside compiled -\ words. If you try to type in expressions using IF, etc. in immediate mode, then they won't work. -\ Making these work in immediate mode is left as an exercise for the reader. - -\ condition IF true-part THEN rest -\ -- compiles to: --> condition 0BRANCH OFFSET true-part rest -\ where OFFSET is the offset of 'rest' -\ condition IF true-part ELSE false-part THEN -\ -- compiles to: --> condition 0BRANCH OFFSET true-part BRANCH OFFSET2 false-part rest -\ where OFFSET if the offset of false-part and OFFSET2 is the offset of rest - -\ IF is an IMMEDIATE word which compiles 0BRANCH followed by a dummy offset, and places -\ the address of the 0BRANCH on the stack. Later when we see THEN, we pop that address -\ off the stack, calculate the offset, and back-fill the offset. +: DEBUGON TRUE DEBUG ! ; +: DEBUGOFF FALSE DEBUG ! ; + +\ CONTROL STRUCTURES ---------------------------------------------------------------------- + : IF IMMEDIATE ' 0BRANCH , \ compile 0BRANCH HERE @ \ save location of the offset on the stack @@ -93,10 +72,6 @@ SWAP ! ; -\ BEGIN loop-part condition UNTIL -\ -- compiles to: --> loop-part condition 0BRANCH OFFSET -\ where OFFSET points back to the loop-part -\ This is like do { loop-part } while (condition) in the C language : BEGIN IMMEDIATE HERE @ \ save location on the stack ; @@ -107,20 +82,12 @@ , \ compile the offset here ; -\ BEGIN loop-part AGAIN -\ -- compiles to: --> loop-part BRANCH OFFSET -\ where OFFSET points back to the loop-part -\ In other words, an infinite loop which can only be returned from with EXIT : AGAIN IMMEDIATE ' BRANCH , \ compile BRANCH HERE @ - \ calculate the offset back , \ compile the offset here ; -\ BEGIN condition WHILE loop-part REPEAT -\ -- compiles to: --> condition 0BRANCH OFFSET2 loop-part BRANCH OFFSET -\ where OFFSET points back to condition (the beginning) and OFFSET2 points to after the whole piece of code -\ So this is like a while (condition) { loop-part } loop in the C language : WHILE IMMEDIATE ' 0BRANCH , \ compile 0BRANCH HERE @ \ save location of the offset2 on the stack @@ -136,23 +103,48 @@ SWAP ! \ and back-fill it in the original location ; -\ UNLESS is the same as IF but the test is reversed. -\ -\ Note the use of [COMPILE]: Since IF is IMMEDIATE we don't want it to be executed while UNLESS -\ is compiling, but while UNLESS is running (which happens to be when whatever word using UNLESS is -\ being compiled -- whew!). So we use [COMPILE] to reverse the effect of marking IF as immediate. -\ This trick is generally used when we want to write our own control words without having to -\ implement them all in terms of the primitives 0BRANCH and BRANCH, but instead reusing simpler -\ control words like (in this instance) IF. : UNLESS IMMEDIATE ' NOT , \ compile NOT (to reverse the test) [COMPILE] IF \ continue by calling the normal IF ; -\ COMMENTS ---------------------------------------------------------------------- -\ -\ FORTH allows ( ... ) as comments within function definitions. This works by having an IMMEDIATE -\ word called ( which just drops input characters until it hits the corresponding ). +: DO IMMEDIATE + ' >R , ' >R , + ' LIT , HERE @ 0 , ' >R , + HERE @ +; + +: I RSP@ 3 - @ ; + +: ?LEAVE IMMEDIATE + ' 0BRANCH , 13 , + ' R> , ' RDROP , ' RDROP , + ' LIT , HERE @ 7 + , ' DUP , ' -ROT , ' - , ' SWAP , ' ! , + ' BRANCH , + 0 , +; + +: LEAVE IMMEDIATE + ' LIT , -1 , + [COMPILE] ?LEAVE +; + +: +LOOP IMMEDIATE + ' R> , ' SWAP , ' R> , ' SWAP , ' R> , ' SWAP , ' + , ' 2DUP , ' - , + ' SWAP , ' >R , ' SWAP , ' >R , ' SWAP , ' >R , + ' 0<= , ' 0BRANCH , + HERE @ - , + ' RDROP , ' RDROP , ' RDROP , + HERE @ SWAP ! +; + +: LOOP IMMEDIATE + ' LIT , 1 , + [COMPILE] +LOOP +; + +\ COMMENTS ---------------------------------------------------------------------- + : ( IMMEDIATE 1 \ allowed nested parens by keeping track of depth BEGIN @@ -169,23 +161,9 @@ DROP \ drop the depth counter ; -( - From now on we can use ( ... ) for comments. - - STACK NOTATION ---------------------------------------------------------------------- - - In FORTH style we can also use ( ... -- ... ) to show the effects that a word has on the - parameter stack. For example: - - ( n -- ) means that the word consumes an integer (n) from the parameter stack. - ( b a -- c ) means that the word uses two integers (a and b, where a is at the top of stack) - and returns a single integer (c). - ( -- ) means the word has no effect on the stack -) - ( Some more complicated stack examples, showing the stack notation. ) : NIP ( x y -- y ) SWAP DROP ; -: TUCK ( x y -- y x y ) DUP ROT ; +: TUCK ( x y -- y x y ) DUP -ROT ; : PICK ( x_u ... x_1 x_0 u -- x_u ... x_1 x_0 x_u ) 1+ ( add one because of 'u' on the stack ) PSP@ SWAP - ( add to the stack pointer ) @@ -194,47 +172,39 @@ ( With the looping constructs, we can now write SPACES, which writes n spaces to stdout. ) : SPACES ( n -- ) - BEGIN - DUP 0> ( while n > 0 ) - WHILE - SPACE ( print a space ) - 1- ( until we count down to 0 ) - REPEAT - DROP + 0 DO + SPACE + LOOP ; ( Standard words for manipulating BASE. ) : DECIMAL ( -- ) 10 BASE ! ; : HEX ( -- ) 16 BASE ! ; -( - PRINTING NUMBERS ---------------------------------------------------------------------- - - The standard FORTH word . (DOT) is very important. It takes the number at the top - of the stack and prints it out. However first I'm going to implement some lower-level - FORTH words: - - U.R ( u width -- ) which prints an unsigned number, padded to a certain width - U. ( u -- ) which prints an unsigned number - .R ( n width -- ) which prints a signed number, padded to a certain width. - - For example: - -123 6 .R - will print out these characters: - - 1 2 3 - - In other words, the number padded left to a certain number of characters. +( Compute absolute value. ) +: ABS ( n -- |n| ) + dup 0< if + negate + then +; - The full number is printed even if it is wider than width, and this is what allows us to - define the ordinary functions U. and . (we just set width to zero knowing that the full - number will be printed anyway). +: MAX ( n m -- max ) + 2dup - 0< if + swap drop + else + drop + then +; - Another wrinkle of . and friends is that they obey the current base in the variable BASE. - BASE can be anything in the range 2 to 36. +: MIN ( n m -- max ) + 2dup - 0> if + swap drop + else + drop + then +; - While we're defining . &c we can also define .S which is a useful debugging tool. This - word prints the current stack (non-destructively) from top to bottom. -) +( PRINTING NUMBERS ---------------------------------------------------------------------- ) ( This is the underlying recursive definition of U. ) : U. ( u -- ) @@ -254,4 +224,101 @@ EMIT ; +( This word returns the width (in characters) of an unsigned number in the current base ) +: UWIDTH ( u -- width ) + BASE @ / ( rem quot ) + ?DUP IF ( if quotient <> 0 then ) + RECURSE 1+ ( return 1+recursive call ) + ELSE + 1 ( return 1 ) + THEN +; + +: U.R ( u width -- ) + SWAP ( width u ) + DUP ( width u u ) + UWIDTH ( width u uwidth ) + ROT ( u uwidth width ) + SWAP - ( u width-uwidth ) + ( At this point if the requested width is narrower, we'll have a negative number on the stack. + Otherwise the number on the stack is the number of spaces to print. But SPACES won't print + a negative number of spaces anyway, so it's now safe to call SPACES ... ) + SPACES + ( ... and then call the underlying implementation of U. ) + U. +; + +: .R ( n width -- ) + SWAP ( width n ) + DUP 0< IF + NEGATE ( width u ) + 1 ( save a flag to remember that it was negative | width n 1 ) + -ROT ( 1 width u ) + SWAP ( 1 u width ) + 1- ( 1 u width-1 ) + ELSE + 0 ( width u 0 ) + -ROT ( 0 width u ) + SWAP ( 0 u width ) + THEN + SWAP ( flag width u ) + DUP ( flag width u u ) + UWIDTH ( flag width u uwidth ) + ROT ( flag u uwidth width ) + SWAP - ( flag u width-uwidth ) + + SPACES ( flag u ) + SWAP ( u flag ) + + IF ( was it negative? print the - character ) + '-' EMIT + THEN + + U. +; + +: . 0 .R SPACE ; + +: .S ( -- ) + '<' EMIT DEPTH U. '>' EMIT SPACE + PSP0 @ 1+ + BEGIN + DUP PSP@ 2 - <= + WHILE + DUP @ . + 1+ + REPEAT + DROP +; + +: U. U. SPACE ; + +( ? fetches the integer at an address and prints it. ) +: ? ( addr -- ) @ . ; + +( c a b WITHIN returns true if a <= c and c < b ) +: WITHIN + -ROT ( b c a ) + OVER ( b c a c ) + <= IF + > IF ( b c -- ) + TRUE + ELSE + FALSE + THEN + ELSE + 2DROP ( b c -- ) + FALSE + THEN +; + +: ROLL ( x_u x_u-1... x_0 u -- x_u-1 ... x_0 x_u ) + 1+ DUP PICK SWAP ( x_u x_u-1 ... x_0 x_u u+1 ) + PSP@ 1- SWAP - PSP@ 2- SWAP + DO + i 1+ @ i ! + LOOP + SWAP DROP +; +